APPLICATION OF TIME-SERIES ANALYSIS FOR THE RECOGNITION OF INCREASES IN URINARY ESTROGENS AS MARKERS FOR THE BEGINNING OF THE POTENTIALLY FERTILE PERIOD

Time-series analysis was applied to the urinary total estrogen data from 142 ovulatory menstrual cycles to determine the first statistically significant increase as a marker for the beginning of the potentially fertile phase. Application of the Trigg's tracking signal to each cycle detected an increase in urinary total estrogens above the baseline in every case, with a cumulative probability of greater-than-or-equal-to 95%. The distribution of first increase days ranged from 10 days before to 3.5 days before the presumed day of ovulation with a mean of 6.5 +/- 1.4 days. The significant parameters in the calculation of the tracking signal are the smoothing constant (alpha) which is related to the number of baseline observations, the baseline mean for the cycle, and the variation of the baseline mean. The method allows a calculation of the tracking signal as the cycle unfolds and a statistical assessment can be given each day. The procedure is easily adaptable for computer calculation, and because it is applied to individual cycles avoids the use of population means with the loss of information inherently associated with the combination of data from many cycles. The Trigg's tracking signal is an appropriate method of analysis of menstrual cycle data and represents a satisfactory alternative to the more usual cumulative sum procedure. The distribution of the first increases constitutes a reference standard for urinary estrogen assays.